This is quite a common advice that many people give to others. It sounds very nice but is it always practicable for everyone? Practically, happiness may mean different to different persons depending on several factors.
Life is not the same for everyone. Nature has not distributed everything equally. Without getting in to the cause and logic of inequality, bitter fact is that hunger, poverty, sickness and above all the helplessness takes away all the joy, happiness and positivity. A person dying of hunger knows nothing other than food exactly like a sick person needs medicine not a lecture or ride on an expensive motor vehicle. The one feeling unsafe needs safety and security that doesn’t come through hollow statements and slogans. You call it positivity or negativity, the choice is yours but ask the sufferers who can do nothing other than crying. Crying is negative, fine but what else the person can do when choked from all directions? There is plenty of poverty and helplessness in the world. Is this advice practicable for those dying in the hospitals without medicine, for those who have to go without food for days and days, for those who starve and feel compelled to sell their children? Laughter and joy are not for everyone and I am sure we all know it.
Humanity, positivity, happiness, calmness and flowery logic are not for everyone in all situations. The rich and the elite class has no difficulty in being happy and positive but these words become meaningless for those who suffer everyday, every moments of their life. Fun is not for those who feel the pinch, not once or twice but through every moment of their life. These are cruel and very hard facts. Seeing what is happening to the helpless particularly in poor countries, sensitive persons forget even to smile leave alone laughing and being positive.
The requirement is to help the needy as much as you can, try to solve their genuine problem and then advise them to be happy and positive. Short of that, such advice would be nothing more than a formality.